Mycobacterium tuberculosis is the largest single infectious disease killer in the world today. Its penetrance of the human population is due its ability to cause persistant infections in the human host. Work from our laboratory and several other labs have reported enhanced levels of isocitrate lyase expression in intracellular or dormant bacilli. Isocitrate lyase is the first enzyme of the glyoxylate shunt pathway which exploits acetate or long chain fatty acids as an alternate carbon source. ICL competes with isocitrate dehydrogenase to divert the flux of carbon away from the TCA cycle and into this alternative pathway of carbon acquisition. We propose to examine the role of the glyoxylate shunt and its potential as a drug target. These are the specific goals of this project. 1. Identification of the environmental stimuli responsible for upregulation of ICL expression. We will examine the culture conditions required to induce maximal expression of ICL. In addition we will use the icl promoter to drive expression of ICL: GFP and LacZ constructs to probe the intracellular environment to determine what effect changes in immune status have on ICL expression. 2. The role anaplerotic m abolism in sustaining a latent infection. We shall use both the ICL: GFP construct and antibodies against ICL and malate synthase to probe the expression of these enzymes in murine infections. This work will be undertaken in collaboration with Dr McKinney in different KO mice with different mycobacterial mutants. 3. Identification of compounds inhibitory to ICL and malate synthase activities and their development as antimycobacterial agents. We will use the recombinant enzymes to screen drug libraries at GlaxoWellcome. Structural information generated by Dr. Sacchettini will be central to the development of effective inhibitors against these enzymes.